The 2015 plan didn’t pan out because Larry Scott went at it alone and the existing TV deals didn’t facilitate the process. The PAC may have lame fan bases but Washington, Oregon, USC, and ASU have strong fan bases that drive a lot of value.
Poaching poses legal challenges and burns bridges and ties between the two conferences that are 100 years old. Merging creates travel and logistical issues. But partnering on media rights creates the best of both worlds because the best content can be selected before hand and it provides market reach for both into new areas. This scenario would be awful for the ACC and Big 12, but it doesn’t mean it is a bad idea.